Graphene, single-layer sheets of pure carbon with the atoms arranged in a hexagonal pattern, is relatively novel as a material of broad interest and potential. Graphene is one of the thinnest, strongest, and stiffest materials known, and is also an excellent conductor of both heat and electricity. Graphene sheets are, however, insoluble in many common organic solvents and indispersible in many polymers without further treatment of the graphene.
For many applications, a simple and facile preparation of graphene dispersions in organic media is a desirable prerequisite for the development of scalable solvent-assisted graphene processing, including surface spin-coatings, inkjet-printing on plastic substrates, graphene films or papers, and conducting displays for applications in nanoelectronics, nanophotonics, electric devices, and sensors. It is also desirable to have the ability to homogenously disperse graphene in polymers, and to achieve good affinity with the polymers for the development of applications such as graphene-based polymer composites and active graphene layers for organic electronic elements. A dispersion of graphene oxide or graphene at as low as 0.05 wt % in a polymer matrix could result in exceptional enhancements in electrical conductivity and mechanical properties.
One general method for formation of graphene is commonly referred to as a “bottom-up” production in which graphene may be obtained by chemical vapor deposition, or from micro-mechanical cleavage of graphite wherein single graphene layers are pulled off the graphite. An alternate approach, referred to as a “top-down” approach, involves the oxidation of graphite to form graphite oxide, followed by exfoliation and reduction of the graphite oxide. However, the toxic reducing agent hydrazine is commonly used in this process, and may result in incompletely exfoliated graphene sheets which cannot effectively interact with the host media. In addition, the exfoliated sheets may tend to restack or even reform graphite after reduction has taken place.
Cost-effective and mass production strategies for simple and facile exfoliation and effective reduction and surface modification of graphene sheets are desirable for improved top-down preparations.